Red Bull's technical chief Adrian Newey believes his team will be affected "quite heavily" by the ban on off-throttle diffusers that comes into effect from this weekend's British Grand Prix.
"I think we will be quite heavily affected because our car was designed around the exhaust in as much as it was part of the design right from the outset," Newey told news agency Reuters.
"Probably with the exception of Renault and ourselves everybody else has generally speaking copied someone else's principal, mainly ours, and adapted to the car that they had pre-season.
"So it might therefore be, because our car has been designed around it, it's going to be more of a hit for us but it's very difficult to forecast."
Newey also admitted he was mystified as to why the FIA has decided to ban something that had been legal up until now.
"I'm slightly baffled by it because it's been declared legal forever until this race," he added.
"The obvious parallel is when active suspension was banned at the end of '93, where there was no regulation change. Ferrari couldn't get their active to work and suddenly it was illegal for the next year.
"It's easy to fall into the Machiavellian conspiracy theories. Whether that's true or not, I don't know and I can't comment. My read of it would be that, of our main competitors, which are clearly McLaren and Ferrari, then Ferrari probably haven't got their exhaust to work that well so they are quite happy to see the back of it.
"McLaren probably don't know whether they are going to lose more or less than us. But probably on the basis that they could probably do with a wild card thrown into the pack, they are probably relieved to have something that is different," he added.